chore: add generation config #6853

Job	Run time
build(21) except self-service clients	11m 40s
build (11)	12m 43s
build(8) except for gapic-generator-java	3m 55s
build (17)	12m 22s
build(8) for gapic-generator-java	9m 41s
compatibility	1m 35s
dependency_analyzer_unit_test	16s
gapic-generator-java-bom	1m 40s
lint	36s
showcase (11)	4m 6s
showcase-clirr	3m 8s
showcase (17)	4m 10s
showcase-native	8m 15s
unmanaged_dependency_check	4m 45s
	1h 18m 52s

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